The effect of hydrogen on crack growth in X70 pipeline steel under cyclic low-frequency load

• A.I. Marshakov and V.E. Ignatenko

Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 31-4, Leninsky prospect, 119071 Moscow, Russia

Abstract: The purpose of this work was to determine the dependence of the crack growth rate (CGR) in X70 pipe steel under low-cycle loading on the rate of hydrogen permeation through the steel membrane. The measurements were conducted in a neutral NS4 solution at various electrode potentials of steel. The load parameters were varied as follows: the maximum values of the stress intensity factor at the crack tip (K_max) ranged from 16 to 45 MPa·m^0.5, the amplitude of load variation (ΔK) ranged from 8 to 22 MPa·m^0.5, and the cycle frequency (f) was 0.01 or 0.005 Hz. It was shown that the dependence of the CGR on the cathodic potential had a minimum if the values of the combined factor ΔK^0.67·K_max^0.33/f^0.033 did not exceed a threshold value. The critical values of the steady-state hydrogen permeation current densities (ip,cr) through the steel membrane, at which the crack growth accelerates, were determined. It was shown that an increase in the combined load parameter factor ΔK^0.67·K_max^0.33/f^0.033 by a factor of three led to a decrease in i_p,cr by approximately 10 times. The obtained values of i_p,cr can be used to determine the risk of hydrogen damage in underground pipelines using membrane-type hydrogen sensors. The effective diffusion coefficient of hydrogen in X70 steel was determined during cathodic polarization in NS4 solution, and the hydrogen concentrations in the metal corresponding to the values of i_p,cr were calculated. These concentrations were compared with the literature data on the solubility of hydrogen in pipeline steel under elevated pressure of gaseous hydrogen.

Keywords: X70 pipe steel, stress corrosion cracking, crack growth rate, hydrogen embrittlement monitoring

Int. J. Corros. Scale Inhib., 2026, 15, no. 2, 346-363
doi: 10.17675/2305-6894-2026-15-2-20

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